What made him so interested in the heart... Why did he do those experiments to begin with.
This is explained in the Ansem Reports?
DiZ was spurred to investigate the heart because he saw what darkness was doing to the residents of Radiant Garden and wanted to prevent the world itself from falling, and because he was interested in trying to cure Xehanort's Amnesia.
"Much of my life has been dedicated to the pursuit of knowledge. That knowledge has guarded this world well. Not a soul doubts that. I am blessed with my people's smiles and respect.
But though I am called a sage, there are things I do not understand.
I believe that Darkness sleeps in every heart, no matter how pure. Given the chance, the smallest drop can spread and swallow the heart. I have witnessed it many times.
Darkness..
Darkness of the Heart.
How is it born?
How does it come to affect us so?
As ruler of this world, I must find the answers.
I must find them before the world is lost to those taken by the Darkness."
--Ansem Report 1, written by DiZ
Is he a keyblade wielder...
No, hence his confusion as to how Xehanort could open the door to Radiant Garden's heart.
Is he going to meet young xehanort and young Eraqus briefly, in time so that he wouldn't recall his name when Terranort told him when he fell in radiant garden with aqua's armor!
I mean... wouldn't it be easier and simpler for the story for him to have just never have met them?
I really want to see a major role being played by ansem the wise in kingdom hearts 3! I just see it happening! Doesn't anyone agree?!
Well, I'd like for him to have some purpose, personally. I don't think it's going to be a major role though, like, aside from his past actions being relevant (i.e. I think the data he hid in Sora is going to be important, but present day!DiZ may not have a major role to play in the current story)